It is used notably in the field of telecommunications using an OFHMA (Orthogonal Frequency Hopping Multiple Access) waveform.
In the field of telecommunications using waveforms of OFHMA type, orthogonality is usually ensured by time distribution and maintenance of master-slave type which contrives matters such that the instants of arrival of all the carriers sent by the ground segment in the same repeater are synchronous at the satellite, doing so with a synchronization precision that is much better than the duration of the dead time of the FH (frequency hopping) waveform. This guarantees zero self-jamming of the network and therefore better network capacity. The time management is therefore of centralized type.
The means generally used to fulfill the above orthogonality condition is a slaving loop between the timing master of the network and each subscriber (slave) of the network.
Given the latency of the slaving loop, any Transit Time variation due to the motion of the satellite (for example, the inclination of a few degrees of the orbital plane which creates the famous “eight” of the satellite) or of the carrier (for example, the speed of the vessel) in a 1st-order control loop manifests itself as a steady state with a loop error incompatible with the synchronization precision demand required by the orthogonality condition.
The dual problem to be solved is therefore to ensure a satisfactory loop convergence time, at the same time as a zero or quasi-zero steady state loop error, with a correct stability margin. Specifically, the convergence time of this control loop is a predominant element in a station's network re-entry time performance.
It is known from the prior art to use second-order slaving to zero this loop error. However, this is done to the detriment of the convergence time of the loop which will increase significantly to maintain a sufficient stability margin of the slaving loop. The drawbacks of the second-order slaving solution are notably its complexity and principally the lengthening of the convergence time.
Significant overshoot with a great deal of chatter may also arise for certain adjustments of loop gains.